Interestingly, the human brain has been increasing in size since the 1930s. According to scientists, a larger brain size is associated with better health and improved cognitive functions. Researchers at the University of California, Davis, have explored how this change affects the risk of developing dementia.
A Brief History of the Issue
In 2020, over 55 million people worldwide were living with dementia. Experts expressed concerns that this number could double every 20 years. However, the rising prevalence of this condition likely reflects the aging global population and the fact that people are living longer. A study conducted by the National Institutes of Health (NIH) in 2016 revealed a gradual decline in new cases of dementia since the 1970s, averaging a 20 percent decrease per decade.
But what contributes to this decline? Among other factors, researchers examined the impact of education on dementia risk. They found that, compared to the 1970s, the incidence of dementia had decreased by 44 percent among individuals with at least a high school education by the turn of the millennium. While the study identified a link between education and dementia, it did not address potential underlying causes.
Insights from the Authors of the New Study
“Genetics play a significant role in determining brain size, but our findings suggest that external factors, such as health, social, cultural, and educational influences, may also play a part,” said Charles DeCarli, a professor of neurology, director of the Alzheimer’s Disease Research Center at the University of California, Davis, and the lead author of the study.
His team utilized the same dataset that was studied previously—the Framingham Heart Study (FHS). Launched in 1948, this extensive study involved over 15,000 participants from Framingham, Massachusetts, spanning three generations of volunteers. The goal was to identify trends in brain and heart health, as reported by New Atlas.
From 1999 to 2019, researchers examined brain scans of 3,226 individuals (53% women and 47% men) obtained through MRI. All participants were born between 1930 and 1970, and none had a history of cognitive impairment or stroke, which increases the risk of developing dementia.
When researchers compared the scans of individuals born in the 1930s with those born in the 1970s, they observed a gradual yet consistent increase in the size of certain brain structures. For instance, the intracranial volume (ICV) increased from an average of 1,234 ml (41.7 fluid ounces) in those born in the 1930s to 1,321 ml (44.7 fluid ounces) in those born in the 1970s—an increase of 6.6 percent.
Between these generations, there was also an increase in the volume of white matter (by 7.7 percent) and gray matter in the cerebral cortex (by 2.2 percent). Additionally, the volume of the hippocampus, which is primarily responsible for storing short-term memories and transferring them to long-term storage, increased by 5.7 percent. Meanwhile, the surface area of the cortical layer, the wrinkled visible layer of gray matter, expanded by 14.9 percent.
The increase in brain structures may indicate improved brain development and health, according to Professor DeCarli. A larger brain size provides a greater reserve, which may help mitigate the effects of age-related diseases such as Alzheimer’s and associated dementia.
Researchers acknowledge that genetics play a significant role in an individual’s cognitive health. However, they believe that environmental factors during early life influence the increase in brain structures and the reduction in dementia risk. The observed trend of increasing brain structures likely reflects improvements in health, education, and sociocultural factors since the 1930s.
The study’s findings were published in JAMA Neurology.